According to "The Home Energy Diet" by Paul Scheckel, which I'm currently reading, there was a study done at a German university on this. They had volunteers wash 12 place settings and also had a dishwasher do the same. The results were:
| . | Volunteer | Dishwasher |
| Water usage | 27 gallons | 4 gallons |
| Water Heating | 2.5 kWh | 1.5 kWh |
I found this pretty interesting. I didn't think hand washing was THAT much less efficient. It also states that "about the dishes were were judged to be 'really dirty' or at least not acceptable to be placed on a dinner table, while the machine dishwashers offered consistently cleaner dishes".